This application is related to the application for a PRIMER BULB RETAINER FOR CARBURETOR by Thomas G. Guntly et al and assigned to a common assignee, filed on even date herewith, Serial No. 590,350, filed Sept. 28, 1990.
The subject invention is generally related to carburetors for internal combustion engines and is specifically related to a floatless carburetor equipped with an integral primer feature.
The simplest carburetor designs utilize the fuel tank as the carburetor reservoir wherein the fuel is drawn up through a tube from the fuel tank directly into a venturi via a metering orifice in the carburetor throat and from the throat directly into the engine. An example of such a carburetor can be found on the Briggs & Stratton Model 929 engine. More complex designs utilize an independent fuel feed reservoir separate from the main fuel tank, in combination with an impulse type fuel pump which reacts to the change in pressure due to the cycling of the engine to draw fuel from the main fuel tank into the reservoir. An example of this type of carburetor can be found on the Briggs & Stratton Model 929 engine. This type of design is in part, similar in function to float type carburetors where the level in a fuel feed reservoir is controlled by a float and inlet valve.
In floatless carburetors, the level in the reservoir is controlled by an overflow channel provided in the reservoir for dumping excess fuel back into the main fuel tank. The primary distinction between float type and floatless carburetors is that the float system is operative to regulate and intermittently shut off incoming fuel when the fuel level in the fuel feed reservoir is at a pre-selected level. In the floatless carburetor, the fuel pump continually pumps fuel from the tank into the fuel feed reservoir and excess fuel is dumped from the reservoir back into the tank through an overflow. Reservoir type carburetors are recognized as an advance in the art over carburetors drawing the fuel directly from the main fuel tank to the venturi because the reservoir permits the carburetor to operate on a constant fuel level system similar to float feed carburetors, whereby changes in tank fuel levels do not affect fuel metering.
Float fuel carburetors within float controlled fuel feed reservoir levels are generally considered superior in performance because of this reservoir control. However, the additional cost in the manufacture and design of float feed carburetors over floatless carburetors makes them less desirable in certain applications, particularly for small internal combustion engines. This is largely due to a combination of fuel tank, fuel hoses, fuel clamps and additional assembly required. While floatless carburetors are known and currently used, the prior art designs have not achieved the standards of performance commonly associated with float feed carburetors.
Both float feed and floatless carburetors, typically require either choking or priming prior to starting in either cool weather or after period of non-operation in order to enrich the air/fuel mixture. Typically, the carburetor and fuel delivery system includes either a choke mechanism or a primer system. On float feed carburetors, the primer generally comprises a compressible resilient bulb in communication with a closed chamber wherein depression of the bulb compresses either forcing fuel directly from the bulb or compressing air which in turn forces fuel from the chamber into the induction tract. The fuel so introduced enriches the fuel air mixture for enhancing cold starting of the engine.
The main drawback of prior art floatless reservoir concepts has been that where the reservoir of a float carburetor is always filled for immediate starting, floatless reservoirs can be empty either on initial start or after running the tank empty of fuel and restarting. In these prior art reservoir carburetors, in order to fill the reservoir, the pump must be actuated by attempting to start the engine resulting in as high as 8-10 pulls of the starter rope.
A combined carburetor and impulse fuel pump is disclosed in the U.S. Pat. No. 4,168,288 to Nau et al issued Sept. 18, 1979. A float type carburetor with an integral primer system is disclosed in the following U.S. patents all issued to Guntly or Guntly et al: U.S. Pat. Nos. 4,679,534 issued July 14, 1987; 4,684,484 issued Aug. 4, 1987 and 4,735,751 issued Apr. 5, 1988. An example of a conventional float type carburetor with an integral priming system is disclosed in the Altenbach U.S. Pat. No. 4,197,825 issued Apr. 15, 1980.